EFFECT OF GAMMA RAYS RADIATION ON THE BACTERIOLOGICAL QUALITY OF ICE CREAM

Abstract

In this study, 100 samples of ice cream which were divided into 2 groups (50 vanilla and 50 chocolate) collected individually from different supermarkets in Mansoura city, Egypt, for sensory and bacteriological examination before subjection for radiation, then each group was divided into 2 subgroups and exposed to radiation. The 1st subgroup from the 2 groups was exposed to 2 KGy of gamma rays and the 2nd subgroup from the 2 groups was exposed to 3 KGy of gamma rays. After the radiation exposure, all the subgroups were subjected to sensory and bacteriological examination to detect the counts of aerobic plate bacteria; Staph. aureus; Bacillus cereus and coliforms. For the vanilla samples before radiation, the counts were 1.8x104 ± 0.14x102, 0.28x102 ± 0.095x102, 2.2x102 ± 0.4x102 and 1.6x102 ± 0.06x102 cfu/ ml respectively, and the counts after radiation in the 1st subgroup were 1.7x103 ± 0.03x102, 0.06x102 ± 0.04x102, 0.6x102 ± 0.13x102 and 0.06x102 ± 0.026x102 cfu/ml respectively, and in the 2nd subgroup were 0.7x102 ± 0.07x102, ND (not detected), 0.08x102 ± 0.07x102 and ND cfu/ml respectively. For the chocolate samples before radiation, the counts were 3.8x104 ± 0.27x102; 0.5x102 ± 0.03x102; 0.8x102 ± 0.15x102 and 1.5x102 ± 0.07x102 cfu/ml respectively, and the counts after radiation in the 1st subgroup were 2.4x103 ± 0.04x102, ND, 0.13x102 ± 0.025x102 and 0.04x102 ± 0.017x102 cfu/ml respectively, and in the 2nd subgroup were 1.6x102 ± 0.026x102, ND, 0.04x102 ± 0.01x102 and ND cfu/ml respectively. About the incidence of the isolated bacteria in the vanilla ice cream samples, E. coli, L. monocytogenes and Y. enterocolitica were before the exposure to radiation in percentages as 12, 10 and 6% respectively, and in the chocolate samples were 10, 8 and 2% respectively. While, after the radiation exposure, non of E. coli, L. monocytogenes and Y. enterocolitica could be isolated from both the vanilla and chocolate samples. In addition, Salmonella typhimurium could not be isolated at all. Therefore, gamma irradiation can be applied at dose of 3 kGy to improve the microbial quality and safety of frozen ice cream products without adverse effects on human health and their sensory acceptability.